Automatic electromagnetic switch



A ril 17, 1951 E. M MULLEN ETAL AUTOMATIC ELECTROMAGNETIC SWITCH Filed Nov. 15, 1948 n S e m m U T M 2 U N I. m H B C N I H MM 1 I 5 .m, m QM NIQ .F .m a 4 A\\\ N v. [1m 50 B mm mm 3 m 4 F 3 5 2 .w m 3 3 Patented Apr. 17, 1951 AUTOMATIC ELECTROMAGNETIC SWITCH Elvin McMullen and Chester A. McMullen,

I Hutchinson, Kans.

Application November 15, 1948, Serial No. 60,046

4 Claims. 1

This invention relates to automatic electromagnetic switches associated with electromotors and the like and more particularly to electromagnetic switches operating in connection with induction motors of the split phase or capacitor type and it has for its main object to provide an automatic switch of very small size which may be mounted within the housing or casing of any induction or other A. C. motor and which is capable of safely handling relatively heavy currents such as those drawn at the starting of an induction motor.

It is a further object of the invention to provide an automatic electromagnetic switch which is of very small thickness so that it extends mainly along one plane and which is entirely contained within the flat casing extending substantially along said plane, all of its magnetic and movable parts being assembled within said casing which is surrounded by an electromagnetic coil responsive to differences in current intensity which correspond to differences of the load.

It is a further object of the invention to provide an automatic electromagnetic switch adapted to operate as a starter switch for split phase or capacitor induction motors, the movable parts of which are essentially located inthe plane along 7 which the core of the electromagnet extends, said core having cut out portions and channels in which the movable parts are located while the core is surrounded by a flattened coil.

It is a further object of the invention to provide an automatic electromagnetic switch having a flat core extending substantially along a plane,

said core having sections cut out at diagonally I opposite corners of the core, said out sections being connected by a channel or passage and the movable contacts of the switch being carried by a member passing through and pivoted within said channel or passage and projectin from said passage into said out out sections, while the fixed contacts are carried by a bent leaf spring fixed to an insulating member carried by the small sides of the core, said contact rod being under the influence of a spring and electrically connected with the core, said core being surrounded by a flat coil connected with the core and with an operating circuit, the circuit controlled by the switch being connected with the fixed contact carried by the said bent spring.

Further and more specific objects will be explained in the detailed specification.

The invention is illustrated in the accompanying drawingshowing one embodiment thereof.

v It will be understood that this embodiment is onl shown by way of example in order to explain the principle of the invention and the best mode of carrying it into effect. Modifications of the example shown are therefore not necessarily departures from the essence of the invention.

In the drawings:

Figure 1 is a perspective view of the automatic switch.

Figure 2 is a sectional elevational view, the section being a longitudinal section along line 2-2 of Figure 3.

Figure 3 is an elevational cross sectional view, the cross section being taken along line 3-3 of Figure 2.

Figure 4 is a diagram of the connections of the switch when used as a starter switch for an induction motor.

Figure 5 is a perspective view of a detail.

As above described the automatic switch according to the invention may be used in connection with heavy loads. For instance, the automatic switch according to the invention may be used as a starter switch in induction motors of the so-called split phase type or of the capacitor type.

It may first be pointed out that induction motors of the so-called split phase type have a stator provided with a main winding and further provided with an auxiliary winding, the latter being necessary because, upon starting, the current flowing through the main winding does not produce a torque until the rotor moves, the torque increasing only with the speed which the rotor acquires. Therefore, a starter winding is necessary which is energized simultaneously with the main winding but which is afterwards switched off as soon as the rotor has acquired its full load speed.

It, will also be understood that at standstill the main winding draws a heavy current, as no resistance is. developed and therefore upon starting the motor the current drawn is extremely heavy. As soon as the auxiliary winding thereafter produces rotation of the rotor the current decreases and finally, at approximately full load speed, the normal full load current passes the winding. The current at full load is, as a rule, only a fraction of the initial starting current drawn at standstill. It will also be clear that at full load speed the auxiliary winding should be disconnected as it reduces the efiiciency.

From the above explanation it will be clear that an automatic electromagnetic switch is necessary or desirable controlling the starting phase of the motor operation. This electromagnetic automatic switch has to perform two operations. The first operation consists in switching in the auxiliary winding and this operation has to take place, as explained, upon the surge of current following the closing of the motor circuit. The second operation consists in the cutting out of the auxiliary winding, an operation which takes place when the current has been reduced to the normal current strength for a full load with the induction motor rotating at its normal full load speed. It will also be clear that the automatic starting switch is 'energized at a predetermined overload (exceeding the normal or full load and being in general a multiple thereof) and the switch has moreover to be de-energized at normal load.

The currents drawn at the starting of the motor are rather heavy and are usually about four to five times those of the normal load and therefore switches which are used for starting purposes are mostly cumbersome and form a separate unit.

The switch according to the present invention is however of very small dimensions and completely self-contained with no moving parts outside. Its overall dimensions and especially its thickness are extremely small, the said thickness even in cases of rather large motors never exceeding about one-half of an inch and in many cases being only about half this size. The small dimensions permit to fix the switch within the motor housing even if the motor has not originally been designed for the accommodation of a starter switch. I

The switch according to the invention consists of a core 5 of hardened steel composed of oblong plates 5a and 5?) so cut and disposed that empty spaces 6, 1 result at two diagonally opposed corners of the space occupied by the core. These two core plates face each other along a narrow gap 8 with parallel walls 9 forming a channel or passage leading from one empty section to the other. An armature in the shape of a steel rod H) which is bent or curved passes through the gap or passage 8, one end of said rod projecting into the section 6 while the other projects into the section 1. The armature rod It} is pivoted around a pin. I! which is arranged approximately in the center of the gap or passage 8. The rod may therefore rock around said pivot to a limited extent.

The smaller cut out section I is surrounded by a U-shaped copper strip [2 the sides of which are aligned with the sides of the steel core and are soldered to the same. The cut section I is thus transformed into a closed chamber which is open at the small or front end. A spring 5 is mounted on an insulated strip 34 arranged at one end of the transverse portion of the copper strip l2 which presses against the rod H! and has a tendency to move the end portion of the rod towards the core. The other end of the spring is soldered to the rod.

The armature ill in the shape of a steel rod carries a tungsten contact IE3 at its front end which forms the movable contact of the switch.

On the core a fiber strip 18 is mounted which is held by suitable pins IS on one of the small sides of the core. The fiber strip is of a. length corresponding to the total length of the core 5 and, as it also covers the cut section, it is unsupported along the same. To support it a second small fiber strip 20, provided with notches 4 2| is inserted between the end of the strip l8 and the edge 22 of the cut section 6.

On the said strip a leaf spring 24 which is folded or bent is fixed. The leaf spring may be of U-shape. Preferably the spring is a composite spring and consists of a plurality of super posed leaves. One leg 25 of said U-shaped or folded spring 24 is fixed on the fiber strip [8 by means of a rivet 26 which passes through a contact piece 21 and holds the same on the fiber strip. The contact piece is in the form of an angle piece, one leg behind secured to the fiber strip while the other stands out at an angle thereto. A small clamp 28 serves to hold the leg 25 near its bent end to the strip.

The tungsten contact I! is fixed to the end of the bent leaf spring 24 which cooperates with contact I6 on the steel rod 10.

The core 5 with the above described members mounted thereon is completely covered with an insulation 32 preferably made of insulating paper which has been repeatedly dipped into a fireproof plastic and has been dried and hardened.

This insulating sheet preferably does not cover those portions of the small sides of the core which cover the sections so that the contacts and the spring i5 remain accessible.

Around the core, thus provided with an insulation, a coil is wound, shown as consisting of two layers. However, the number of layers and the dimensions of the wire will vary with the conditions under which the switch is operated. In the example shown the ends of the coil 30 are both on the same side of the core. The wire forming the coil is preferably a heavy copper wire and may be insulated or an insulation may be provided after a layer of the copperv wire has been laid out on the insulation of the core by dipping the entire unit into a plastic insulation which is afterwards dried and hardened.

The entire unit including the coil is then covered with an insulation sheet 35 which may be formed by tape dipped into plastic or by a plastic casing or the like.

The ends of the coil which are on the same side of the core are connected with a lead-in wire 31 and with the core 5 respectively. Preferably the coil wire is soldered to the core 5 at one end. A second lead-in wire 36 is soldered to the core and to the end of the coil. The wire 31 is insulated from wire 36 and also from the core. A further lead-in wire 40 is soldered to the flange 21 of the angle piece which is connected electrically with the rivet 26 holding the bent spring.

The operation of the switch will be clear from the foregoing description. Let it be assumed that the switch is to be used in connection with a squirrel cage split phase induction motor 44 the main winding 45 of which is connected with a suitable outlet 46 of the network.

The starting winding 48 is connected with the main winding 45, as usual, at one end, while its other end is connected with wire 40. Moreover the main winding 45 of the induction motor is connected with lead 31 while wire 36 is soldered to the other end of the coil 30 which is connected to the outlet 46.

One of the conductors 41, 49 contains a switch 50.

When switch 50 is closed a current surge through winding 45 will result when the motor is at a standstill. The heavy current drawn by. the winding 45 when the rotor is at standstill.

passes coil 30, magnetizing the core 5 and rocking the armature vIll, thus closing the switch contacts l6, [1. The closing of the switch contact switches'in'the starter Winding 48, the motor starts to rotate, the current through coil 39 drops to a fraction of its original value, the rod l0 therefore drops back under the influence of spring 15 and the starter winding is again out out.

It will of course be clear that the switch may equally well act as anoverload switch, operating a relay circuit which cuts out a phase conductor in the known manner whenever an overload occurs. Alternatively the switch may be used for obtaining the reversal of the direction of rotation or for similar purposes.

While the switch has been described in specific terms it will be clear that constructive changes not interfering with the function operation or shape of the switch will not cause a material change of the latter.

claimed as new is:

1. An electromagnetic switch, operable under load, for automatic operation by a material load increase in the load circuit, comprising a flat coil encircling an elongated prismatic space of a cross section forming an elongated rectangle, a fiat core assembly within said prismatic space consisting of core plates diagonally disposed within said elongated space, said plates being of substantially rectangular shape facing each other across a gap, a movable pivotally mounted armature passing through said gap between the core plates, a contact member on said armature, an insulating strip fixed to one of the core members and projecting therefrom, a fixed contact mounted on said insulating strip, cooperating with the contact member carried by the armature, one of said core plates being connected electrically with the said armature and with one end of said fiat coil, a biasing means for said movable armature and means for connecting the ends of the coil with the load circuit and the fixed contact of the insulating strip with the circuit to be closed in the case of load increase.-

2. An electromagnetic switch, operable under load, for automatic operation by a material load increase in a load circuit, comprising a fiat coil enclosing an elongated prismatic space having an elongated rectangular cross section, a fiat iron core assembly within said coil consisting of flat core plates facing each other across a gap with parallel walls and diagonally disposed within said rectangular prismatic space, each core plate filling only a portion of the length and height of the rectangular prismatic space in the interior of the coil, thus leaving diagonally disposed empty spaces within the rectangular prismatic space'encircled by the coil, a movable pivotally mounted armature passing from one of said empty spaces to the other through the gap between the said core plates, a contact member on said armature, an insulating strip fixed to one of said core. plates, carrying a further contact cooperating with the aforesaid contact member on the armature, and projecting into one of said empty spaces in the interior of the coil, a spring fixedly connected with the said movable armature, normally biasing the armature so as to keep the armature contact member and the fixed contact disengaged, means for connecting the contact carried by the insulating strip with a circuit controlled by the switch, a connection between one of the core plates, the end of the flat coil, the armature and one line of 6 the load circuitv and means for connecting the other end of the coil to the other line of the load circuit.

,3.-An-electromagnetic switch operable under load for automatic operation-by a material load increase in a load circuit, comprising a fiat coil surrounding an elongated substantially pris-- matic space, having an elongated substantially rectangular cross section-a core assembly within said coil encircled space, .consisting of substantially rectangular core plates of a thickness equal to that of the space encircled by the coil, diagonally disposed within the space surrounded by the fiat coil and facing each other across a gap with parallel walls, said core plates having a substantially smaller length and width than the rectangular space so as to leave substantially rectangular empty spaces diagonally disposed within the space encircled by the coil, communicating with each other through said gap with parallel walls, a bent armature rod reaching from one of said empty rectangular spaces into the other and passing through said gap between the core plates, pivoted within said gap so as to be capable to assume a position substantially paral-- lel to the walls of the gap, a contact member on, said armature, an insulating strip fixed to oneof said core plates carrying a further contact cooperating with the contact member of the armature and projecting into one of the empty spaces into the interior of the coil, a spring me-- chanically and electrically connected with one of said core plates and with said armature rod, a. connection between one of the core plates and. one end of the flat coil encircling the core plates, means for connecting the end of the coil connected with the aforementioned core plate with one side of the load circuit and the other end of the coil with the other side of the load circuit.-

and further means for connecting the last named side of the load circuit with the further contact carried by the insulating strip.

4. An electromagnetic switch, operable under load, for automatic operation by a material load increase in a load circuit, comprising a fiat coil encircling an elongated prismatic space of a cross section forming an elongated rectangle, a substantially fiat core assembly within said prismatic space consisting of core plates diagonally disposed within said elongated space, said core plates being of substantially rectangular shape facing each other across a gap with parallel walls substantially parallel to one of the diagonals of said elongated rectangular space, said core plates being of smaller length and width than the elongated prismatic space encircled by the coil so as to leave substantially rectangular empty spaces within said coil encircled space, an armature rod passing'through said gap and projecting into said said core plates, a copper shieldcovering one of said empty spaces having its sides aligned with the sides of the, core and fixed on said core for holding the spring on the end of the armature rod, an insulating strip carried by one of said core plates, a bent spring carried by said strip, a contact carried by said bent spring in front of the movable contact carried by the armature rod, a connection between one of the ends of the coil and one of the core plates connected with the armature rod, means for connecting the afore said end of the coil with one of the lines of said load circuit and the other end of the coil with the other line of the load circuit and means for connecting the contact carried by the insulating strip with the last named line of the load circuit.

ELVIN MCMULLEN. CHESTER A. McMULLEN.

8 REFERENCES CITED The following i eferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name I Date 827,269 Struble July 31, 1906 1,426,993 Kardaetz Aug. 22, 1922 

